Electrochemical Impedance Analysis on Effects from Pressurization on Tubular SOFC’s Performance and Electrode Kinetics
Mingyang Gong, November 14, 2023
This study is part of the on-going research focusing on hybrid power system utilizing solid oxide fuel cell and gas turbine (SOFC-GT) for low emission, highly efficient power generation towards stationary and mobile applications. Pressurization of SOFC is known to provide cell-to-system level benefits in terms of improved power density and integration with bottom cycling device. At this point literature data studying the electrochemical behavior of the SOFC as a function of operating pressure is relatively scarce[[1]], especially for tubular configuration which is considered advantageous toward mobile application. In this study, electrochemical performances of anode supported SOFC tubes (courtesy Special Power Sources LLC, OH) in H2 and CH4 fuels are evaluated at 750oC under different pressures (up to 58 psi) to identify corresponding impact on the electrode reaction kinetics. Electrochemical impedance spectroscopy (EIS) is collected with Solartron 1260/PAR 263 or Gamry 3000 electrochemical testing system in 4-point connection measurement to obtain SOFC impedance spectra as Nyquist and Bode plots. EIS together with scanning electron microscopy (SEM) results indicate correlation between cell performance improvement and anode microstructure as impedance associated with gas mass transport/conversion processes are reduced by pressurization. From non-linear, least-square (NLS) cell impedance fitting, equivalent-circuit model (ECM) is used to characterize impedance responses of different electrode processes at various resonance frequency, such as gas-conversion impedance (GCI) at <1Hz due to concentration gradient along flow channel. Particular pressurization impacts on anode and cathode kinetics are differentiated by adjusting respective reactants partial pressures through independent variation of gas component concentration and operation pressure. The analysis suggest anode response is more dynamically driven by pressure change, while for cathode chemical potential of reactant dominates. Overall, the study demonstrates pressurization can effectively boost cell performance by overcoming both fuel-side and air-sides mass-transport limited processes and certain cell configuration and operation parameters can be more favorable for pressurized SOFC operation.